1. Field of Invention
The present invention relates to a control system and a method for operating the system. More particularly, the present invention relates to a run-to-run control system and a run-to-run controlling method.
2. Description of Related Art
Currently, in the semiconductor process, a metrology process for checking the process performance is performed every several process runs. The metrology process includes several measurement categories, such as thickness, depth, uniformity, critical dimension, defect count, film quality etc. When the result of the metrology process of the current tool shows that the process performance is abnormal, a feed-back signal is transmitted to the process controller of the current tool to modify the current process recipe in order to adjust the process performance to be normal. Sometimes, if the performance shifting of the current tool is not serious, a feed-forward signal is transmitted from the current tool to another tool for performing a semiconductor process next to the current semiconductor process in the semiconductor manufacturing procedure. By referring to the feed-forward signal, the performance shifting caused by the current tool can be compensated by the subsequent semiconductor process.
However, the metrology process is not performed for every process run of each wafer since it takes long time to perform the metrology process. Hence, the result of the metrology process does not real-time reflect the timing at which the process performance starts to change due to the variation of the process environment. Even though the feed-back signal used for modifying the current process recipe and the feed-forward signal used for modifying the current process recipe to compensate the previous performance shifting are provided, the modified process recipe does not instantly respond to the change of the process environment. Therefore, the modified process recipe is not the optimal process recipe for the current tool to perform the current semiconductor process on that moment.